Electrical temperature responsive device



y 1960 E. s. SHANLEY 2,945,196

ELECTRICAL TEMPERATURE RESPONSIVE DEVICE Filed Jan. 9, 1957 IJJGMZ INVENTOR. fDh/ARD S. SHANLE) 4 rfoR/VE Vs.

UnitedSftates Patent ice ELECTRICAL TEMPERATURE R SPONSIVE Edward S. Shanley, Kenmore,1N. Y., assignor to Food Machinery and Chemical Corporation, San Jose, Calif.

Filed Jan. 9, 1957, Ser. No. 633,340

z Claims.- (c1. ass-2s) This invention relates to a temperature responsive device and particularly to such a 'devieeuseful in the monitoring of chemicals in storage and during their reactions.

' A variety of chemicals undergo decomposition'upon being exposed to elevated temperatures or to catalytic impurities. This decomposition, which generally is accompanied by the evolution of heat, frequently becomes excessive and even violent in nature. In cases where excessive decomposition occurs, however, it normally is preceded by a series of minor disturbances in the system which take the form of localized and usually slight and temporary temperature fluctuations. These temperature fluctuations serve as warnings of impending major decompositions and accordingly it is important that they be detected early in order that corrective measures, such as addition to the system of stabilizers or in severe cases evacuation of the system, may be taken before wasteful and even dangerous decomposition takes place.

. A temperature responsive device suitable for detecting the described minor. disturbances in chemical systems must be capable of ;detecting slight temperature rises which may exist only temporarily and at isolated points within the system. Furthermore, the device must be such that having responded to the temperature rise it will emit a signal which continues evenv following return of the temperature to normal. It is also itnportant that the 1 temperature responsive device be free of {mechanical moving parts which in 'time'wouldundergo mechanical failure or which mightbe corroded by exposure to strong chemicals. No heretofore available device is known which possesses this combination of characteristics.

It is a feature of this invention to provide a temperature responsive device-which is responsiveto slight temperature rises which occurat isolated points within a chemical system, and which operates without themovement of mechanical parts. 3

such a device which functions continuously after having 2,945,196 Patented July 12, 1960 being melted. The salt hydrate is employed in an electrical system wherein in its substantially non-conductive state it serves to keep an electric circuit open, and after having been melted it -provides a path for flow of electrical current thereby closing the circuit and making possible actuation of a signal mechanism. The various salt hydrates range in melting temperatures from below room temperature to moderately elevated temperatures, thereby making possible the provision of temperature responsive devices whichare actuated at temperatures only slightly above normal storage or reaction temperatures, or at moderately elevated temperatures.

The herein temperature responsive device is a hermetically sealed system, the salt hydrate beingsealed against the atmosphere in a container which may be shaped as desired to fit within a storage or reaction vessel. Melting of the salt hydrate at any point within the device is sufficient to create an electrically conductive path between the electrodes of'the device, and accordingly a rise in temperature at any point within the storage or reaction vessel which is contiguous to the temperature responsive device is suflicient to close the electrical circuit which contains the device.

In the attached drawings:

Fig. 1 is a longitudinal sectional view of a temperature responsive device according to the present invention.

Fig. 2 is an enlarged sectional plan view of the device of'Fig. 1 as indicated by line II--II in Fig. 1.

The temperature responsive device shown in Figs. 1 and 2 includes a mounting plate 10 having a central circular opening 12. Tube 14 is attached to and projects from the plate 10, upper end 16 of this tube being secured around its circumference to the inside edges of the circular opening in plate 10. The tube 14 is sealed at its lower end 18.

Conductor 20 .is disposed within, and projects from open end 12 of, tube 14, being separated from the walls of the. tube by spacers 22, suitably formed of vulcanized rubber. The annular space between the tube 14 and the conductor 20 is filled with a salt hydrate 24. The upper end 1601? tube 14 is closed tothe atmosphere with a sealing member 26, suitably. formed of a vulcanized rubber or plastic, thereby protecting the salt hydrate 24 from loss or gain of water by contact with dry or highly :i i; '50 It is a further feature of this inventiento -provide been exposed even temporarily to a certain critical, elevated temperature. 3 I

In accordance with the above features of this invention, an electrically operative temperature responsive device is provided which is substantially a non-conductor alarm system, a valve system for adding stabilizers to the system or evacuating the vessel in whichi'it is contained, and the like, permitting the signal mechanism to be actuated when a system which is being monitored by the device undergoes even slight or localized temperature uses V The temperature responsive:deyicecomprises a pair of electrodes separated by a, "body of' sal t hydrate which exhibits a major increase in electrical conductivity upon humid atmospheres andalso from contamination by the surrounding environment.

. Tube 14 and conductor 20 form the electrodes of an electrical circuit 28 which includes a source 30 of electrical current and a signal mechanism 32. Tube 14 is connected to the circuit 28 by lead wire 34, whereas conductor 20 is connected to the circuit with lead wire 3,6... Thecircuit remains open so long as the salt hydrate to a liquid 38, it becomesa conductor of electricity thereby creating a path for flow of electricity between electrodes 14and- 20 and permitting the-circuit 28 to close. This causes-the signal mechanism 32, which is connected into circuit28, to operate for example by sounding an alarm,flashing a light, operating a valve which introduces stabilizer into the system being monitored, and the like.

pervious to attack by the environment in which it is to function. The plate 10 likewise preferably is formed of a conductive material, suitably of the same material as 3 that from which the tube 14 :is formed. Alternatively, this mounting plate can be formed of a non-conductive material, in which case lead wire 34 is affixed directly to the tube 14.

4 nating or direct current as desired. The signal mechanism can be any common electrically operated mechanism which operates at -a pro-selected current flow. One such signal mechanism comprises a relay switch which Conductor 20 likewise is .formed of an electrically 5 closes when the resistance of the salt hydrate drops below conductive material,.andsuitably may be in the formof a predetermined level, and which by closing permits an a rod,a;tube-or a wire. This member must be resistant alarm circuit to be completed. A number of other to, attack by the salt hydrate employed, and where it signaling devices will suggest themselves to one skilled protrudes from sealing member 26 outside the tube 14 in the art. I p it likewise should bejresistant to attack bychemicals in The following is illustrative of the change in current thesystem which is to be'monitored. flow which takes place when a salt hydrate within an The spacers 221S6YV6 to separate conductor 21 from electrical circuit melts thereby becoming a substantial the tube 14 thereby avoiding short-circuiting. However, conductorof electricity. Consider a circuit comprising they likewise serve as barriers .to prevent molten salt an alternating current source, a Wheatstone-typebridge,

' hydrate38 .frormfiowing tothe bottom of the tube 14. It 15 a resistance-indicating device, and containing the salt hywill be apparent that the employment of spacers may be (irate Na CrO-4H 'O =as aresistance element of the cirdispensed With,'-in',cases whercthe salt hydrate is tightly 'f- This al hydrate a a resistance in this y packed within the tube .orfor example where the tube tom of 34,600 ohms. its resistance after it has been is ofjparticularly small diameter or length. It is impormelted and thereafter cooled below its melting point, tant that the electrodes of the temperature responsive however,1is about .25 ohms. ,It will be apparent that .devicehe separated by somemeans, however, and spacers this 1384. fold decrease in'resistance in the salt hydrate .22 are fl it d t Perform thi f ti resistance element would cause a large change in the cur It will be apparent that the herein temperature rerent conducted by the system, .-in accordance with Ohms sponsive device can be constructed otherwise than'inthe l=E/R, and w make the System well-suited to form shown in Figs. 1 and2. For example the tube'or actuation of a elfictfically 0Pe1'atedigna1 mechanism- .container 14 can be formed of a non-conductor, in which The herein temperature responsive device is of parcase two conductors will be situated within the tube, beticular interest n detecting :Slight and localiz d, .fiucing separated by the salt hydrate .in obvious fashion. tuatlng temperature rises in .liquid systems, for exam Other constructions for the present device will suggest vP n t estorage of such chemicals ashydrogen peroxide themselves. or liquified petroleum gas, orin gchemicalrreactions such The salt hydrates useful herein are inorganic salts as p racetic acid "oxidation of olefins wherein the temwhich contain water .of crystallization. They are solid, rerature the chemical y m m e maintained bedry=feeling materials which in the absence of free water 10W C tain relatively low levels. However, it also is. are highly resistant to conduction of electrical current. useful in detecting llempefatllre rises and Providing a It .is:imp.ortant herein that they contain substantially no tilluolls signal thereof, illsllch apparatuses as e etecwaterother than water of hydration, in order that'they tors, in the Storage of Solids which are Subject to p have uitably glectrical resistances prior to being taneous reactions withthe ,eVQlutlQn Of heat, andthe like. melted The particular salt hydrate and electrical system em- At temperatures above their melting points the salt ployed will depend on the particular application, with hydrates split on water of crystallization, forming a high- 40 such obvious factors aas the=maximum temperature which lyconductive solution of water and molten salt. Upon th system a f l permittedwo reach, the ghaPe P E below fl'lelr'meltmg P y do 110? reform and size of the system, the 'material within which the 'Salt yd t f p ate mto Z-P y t 'device 'is'tobe employed, and the like determining the comprising a saturated water solution of a portion of the .Choice fv ry r i a ev p oyd "l a phase. of 9 Salt The system mole Having described only typical embodiments of thehere- .remamsconductrve after the salt has cooled, the waterin temperature res onsive device we do not h t b salt solution :being anexcellentcon'ductor of electricity. d th d 1s 0 6 Typical salt hydrates 'and their pertinent physical and 6 to e spec l' but.wlsh tofeserve "resistance properties in an alternating current electrical ollrselves any whlch Ian circuit are shown in Table I which appears below. These Wlthm f 9 'thejonowmg materials and? the other salt hydrates exhibit similar re- What 15 clalmedls:

sistance properties indirect current electrical circuits. Electricany @Pflative "tempgramre responsivg The tableis merely'illustrative .of the materials suitable 'meiicauy videlimi Q P S g 2 electrodes, 3 Salt .for use herein, iandis .not to beconstrued as limiting the hydrate whichsis Substantially-Ya non-Conductor of 619C- scope of this invention. tricity disposed between andain contact with said elec- Table I As Hydrate Resistance Cooled .Me1t;b1g Melted V Salt Hydrate 'lfgnctp l f ,t,'O.' R=0hms t, C. R=ohms 1;, C R==ohms azsqtloflzo 32 as 25,000 32 40. a 27 .330

Ba(OH)z.'8H2O 7s 30 Infinite 79 10 30 12 NarCrOr 41120 as) 34,600 18 29 25 KB. 2&0 .41 .30 4, 400 41 .10 2s 14 1 Reslstances were determined on samples packed in a I.D., 6 long stainless steel test tube which served as an electrode in a conventional Wheatstone bridge circuit. The other electrode was a 5 diameter stainless steel rod'centrally located in the tube'and separated therefrom by the salt hydrate sample. from the atmosphere.

The electrical-circuit Zilcontains an electrical current source 30 :and a-signal mechanism 32. The electrical currcntsource'dt) canprovide tothe system either alter- A rubber gasket was used to seal the tube trodes, and means hermetically sealing said salt hydrate from .Lthe atmospherefsaidsalthydrate being. convertible to a permanently, highly e1ectrically conductive -"system by being melted and retaining a high degree of electrical conductivity upon cooling to a temperature below that temperature at which it melted and become conductive.

2. Electrically operative temperature responsive hermetically sealed device comprising a tubular outer electrode, an inner electrode spaced within said tubular outer electrode, a salt hydrate which is substantially a nonconductor of electricity disposed between and in contact with said electrodes, and means hermetically sealing said salt hydrate from the atmosphere, said salt hydrate being converticle to a permanently, highly electrically conductive system by being melted and retaining a high degree of electrical conductivity upon cooling to a temperature References Cited in the file of this patent UNITED STATES PATENTS 856,162 Kitsee June 4, 1907 2,316,872 Kernen Apr. 20, 1943 2,413,125 Walbridge Dec. 24, 1946 2,477,348 Postal July 26, 1949 2,487,526 Dahm et a1. NOV. 8, 1949 2,495,867 Peters Jan. 31, 1950 2,546,415 Alcock Mar. 27, 1951 2,804,610 Curtis Aug. 27, 1957 

